JPH095310A - Ultrasonic inspection method - Google Patents

Abstract

PURPOSE: To improve the inspection accuracy of an ultrasonic inspection method by making the amplitude of the chirp wave of transmitted waves constant and the frequency transition widths and pulse widths of the chirp waves of a reference wave and transmitted waves the same and, at the same time, by smoothly changing the amplitudes of a probe and an object to be inspected at their start points and end points. CONSTITUTION: Two kinds of FM waveforms which are generated from a personal computer 61 and frequency-modulated in different directions are converted into analog signals by means of a D/A converter 62, amplified to required transmitting power by means of an amplifier 63 for transmission, and transmitted into an object 4 to be inspected as ultrasonic waves from a probe 3. The signals received by the probe 3 are signal-amplified by means of an amplifier 66 for reception and successively converted into digital signals by means of an A/D converter 67. An FIR filter 68 performs a pulse compression process on the digital signals by computing the correlation between the digital signals and a reference wave generated from the computer 61. The computer 61 can arbitrarily set the shapes of the transmitted and reference waves in accordance with a change of program. The output signal of the filter 68, in addition, is displayed on an oscilloscope 70 through a D/A converter 69.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic inspection method for inspecting the inside and outside of a material non-destructively by using ultrasonic waves or measuring the thickness of the material to grasp the state of an object.

[0002]

2. Description of the Related Art FIG. 7 is a functional block diagram of a conventional general ultrasonic flaw detector. In FIG. 7, reference numeral 1 is a synchronization unit that generates and outputs a synchronization signal necessary for each circuit, 2 is a transmission unit that generates a transmission electric signal based on the output signal from the synchronization unit 1, and 3 is a transmission unit 2 from the transmission unit 2. A probe 5 that generates an ultrasonic wave based on a transmission signal and causes the ultrasonic wave to enter the inside of the subject 4 and receives an echo from the inside of the subject and converts the echo into an electric signal is a probe 5 from the probe 3. A receiving unit for amplifying the electric signal, 6 is a receiving unit 5
It is a display unit for displaying an output signal from the.

When inspecting the inside and outside of a material using ultrasonic waves, a device as shown in FIG. 7 is generally used. In such a device, a pulse wave is generally used as a transmission signal waveform. Has been. The shape of the pulse wave is shown in FIG. Further, the amplitude spectrum of the pulse wave is shown by b1 in FIG. From this b1, it can be seen from the shape of the amplitude spectrum of the pulse wave that the amplitude tends to decrease as the frequency f increases. However, the frequency characteristics of a general probe that is actually used (the product of the conversion efficiency of an electric signal during transmission into an ultrasonic signal and the conversion efficiency of an ultrasonic signal during reception into an electrical signal Looking at the characteristics, it is as shown in b2 of FIG. 8B, and the frequency with the highest conversion efficiency (center frequency)
It has a hill-like distribution with a peak at.

The problem here is that b in FIG.
This is the difference in shape between 1 and b2. That is, this difference means that the energy of the transmission pulse has lost a considerable amount of energy in the process of transmitting and receiving the ultrasonic waves of the probe 3, which is a problem. In the transmitter 2 of FIG.
Although a transmission pulse wave having an amplitude of about V is generated, the reception signal obtained by the probe 3 usually depends on the size of the defect but is several mV when the material of the object is steel.
The amplitude is about the degree, which is amplified to about several hundred mV in the receiving section 5. In this amplification process, even small electric noises mixed in the weak received signal before amplification are amplified as they are, and the size of flaws that can be flaw-detected is naturally limited, and smaller flaws become noise. In order to detect flaws without being affected, the amplitude of the transmission pulse must be increased, and if the energy loss due to the poor transmission efficiency of ultrasonic waves by the probe is taken into account, the increase in the amplitude will be considerable. However, it is unrealistic in terms of hardware configuration.

As a means for solving such a problem, an ultrasonic flaw detector as shown in FIG. 9 has been proposed (Japanese Patent Publication No. 3-43586). In the ultrasonic flaw detector of FIG. 9, 7 is a frequency variable circuit that varies the pulse width to the transmission unit 2 in synchronization with the output signal from the synchronization unit 1,
8 is a frequency setting means for outputting a control signal to the frequency variable circuit 7, 9 is a wave number variable circuit for varying the wave number of the output signal of the frequency variable circuit 7, and 10 is a wave number setting for outputting a control signal to the wave number variable circuit 9. It is a means. In the ultrasonic flaw detector having such a configuration, since the transmission frequency and the number of transmission waves can be varied, the transmission wave ((a) in FIG. 10) is near the peak of the frequency characteristic of the probe, that is, the probe. Since it can be transmitted in the frequency range with the best ultrasonic transmission efficiency (Fig. 10
(B)), the energy loss in transmitting and receiving the probe can be small. Furthermore, the transmission wave that is longer in the time axis direction than the pulse wave ((c) in FIG. 10) has higher transmission energy than the conventional pulse wave. After all, the received signal obtained by a transmitted wave with a large transmitted energy with a small energy loss due to the probe is less susceptible to noise.

Further, as a technique for solving the above problem, there is a technique called pulse compression which is well known in the field of radar (Radar handbook, Skolnik et.al., McGraw-Hill.
Inc ,. 1970). As is well known in this technology, a phase-encoded waveform or a frequency-modulated waveform that is long in the time axis direction (called an FM wave) is transmitted as a transmission wave, and the reception waveform and the waveform used for transmission are By performing cross-correlation calculation processing (pulse compression), the width of the received wave in the time axis direction is shortened, and at the same time, a waveform with a sharp amplitude (main lobe) is obtained to reduce noise. FIG. 11D shows the waveform after the correlation processing. If the received waveform is the same as the transmitted waveform, the amplitude of the main lobe in the waveform is (B
T) ^1/2 , and its width is 2 / B. In ultrasonic flaw detection, the reception waveform is not necessarily the same as the transmission waveform, but the larger the pulse width T and the frequency transition width B of the transmission waveform, the larger the amplitude of the main lobe and the frequency transition width. It can be said that the width of the main lobe can be shortened as B is increased. As a result, the deterioration of the resolution in the time axis direction caused by lengthening the time axis direction of the transmitted wave can be eliminated.

The features of a general FM signal waveform will be described with reference to FIG. In the FM signal ((c) of FIG. 11), within the pulse width T, the frequency B and the amplitude shape (see FIG.
1) and (b)) are set independently of each other. FIG. 11D shows the waveform after the correlation processing. As an apparatus to which this technique is applied to ultrasonic flaw detection, Japanese Patent Laid-Open No. 63-
The device proposed in 233369 publication is known.

In the apparatus proposed in this publication, as shown in FIG. 12, the transmission pulse signal b ₁ (b ₂ ) created by the FM signal setting section 21 is about 200 Vp-p from the FM signal transmitting section 22. Is amplified to the amplitude of 1 and transmitted to the ultrasonic probe 3. The ultrasonic probe 3 transmits an ultrasonic pulse to the subject 4 in response to the transmission pulse signal b ₁ (b ₂ ) and receives a reflected wave. The received reflected wave is converted into an echo signal and input to the quadrature detection unit 25. The echo signal is converted into a complex signal by the quadrature detection unit 25, low-frequency conversion is performed in the frequency band, amplified to a predetermined voltage level, and input to the next correlation unit 26. On the other hand, the reference wave setting unit 27
Is the transmission pulse signal b created by the FM signal setting unit 21.
Create a reference signal r ₁ (r ₂ ) using ₁ (b ₂ ),
It is sent to the correlation unit 26 via the reference wave transmission unit 28.
The correlating unit 26 pulse-compresses the echo signal by performing a correlation calculation between the echo signal and the reference signal r ₁ (r ₂ ). The pulse-compressed echo signal d ₁ (d ₂ ) is converted into a time difference time signal by the quadrature modulator 29 and displayed on the display unit 30.

[0009]

In the device (pulse compression device) shown in FIG. 12, the chirp wave (frequency transition width: 1 to 9 MHz, as shown in FIG. 13A) is used.
When a transmission wave and a reference wave are used with a pulse width of 5 μs (the spectrum is shown in (b) of FIG. 13), the waveform after pulse compression is as shown in (c) of FIG. In (c) of FIG. 13, a main lobe having a sharp amplitude is obtained, and a kind of noise called a side lobe is generated around the main lobe. This noise causes S / N deterioration in the detection of defects existing near the bottom surface when, for example, a plate-shaped object is flaw-detected. The cause of this side lobe generation is due to the increase of the ripple in FIG. 13 (b).

The cause of this ripple is due to the silodove in the cut-out window of the chirp wave, and reducing this side lobe reduces the ripple in the chirp wave and eventually leads to the reduction of the side lobe after pulse compression. . A Hamming window or the like has been proposed as a window function for reducing side lobes. FIG. 13D shows the type of window function and FIG. 13E shows its spectrum.

For example, the waveform after pulse compression ((h) in FIG. 13) in the pulse compression apparatus shown in FIG. 12 by the chirp wave ((f) in FIG. 13) cut out by the Hamming window is a waveform with few side lobes. Therefore, good S / N can be secured even in flaw detection of defects near the bottom surface.
However, as shown in (a) and (b) of FIG.
When a window function such as a Hamming window is used, the area of the spectrum becomes small. Therefore, since the energy of the waveform represented by the square of the area becomes small, the transmission energy is reduced, and the waveform before pulse compression is easily affected by noise. In order to prevent this, it is effective to lengthen the pulse width of the chirp wave and increase the transmission energy ((c) of FIG. 14). However, the chirp wave of the chirp wave is included because it includes the following problems. Increasing the pulse width is not a good idea. Furthermore, application of a window function such as a Hamming window to the transmitted wave leads to a narrow band of the transmitted wave, resulting in an increase in the wave number of the main lobe.
This leads to deterioration of resolution during flaw detection.

Now, the reason why the pulse width of the chirp wave cannot be increased will be described. As shown in FIG. 15A, a defect 37 (a flat bottom hole having a diameter of 5.6 mm and a depth of 7 mm from the surface) existing in the vicinity of the surface of the copper 36, which is an object, placed in the water 35 is detected. Considering the case, the defect echo (F echo) received by the probe 3 is amplified to a predetermined voltage level. At this time, the surface reflection echo (S echo) has an extremely large amplitude as compared with the defect echo. , Fig. 15
As shown in FIG. 15B, the saturated state occurs, and the overlapping portion of the S echo and the F echo is lost. Therefore, the main lobe due to pulse compression is smaller than in the case where the pulse widths are short and do not overlap (FIG. It changes and the reproducibility of the F echo is lost, leading to an increase in the dead zone.

The present invention has been made to solve the above problems, and an object thereof is to provide an ultrasonic inspection method capable of improving inspection accuracy.

[0014]

An ultrasonic inspection method according to one aspect of the present invention transmits a chirp wave whose frequency transits within a predetermined pulse width as a transmission wave into a subject through a probe. , The received wave obtained via the probe is correlated with a reference wave consisting of a preset chirp wave, and the state of the subject is grasped by the pulse-compressed signal after the correlation processing. In the acoustic inspection method, the chirp wave used as the transmitted wave has a constant amplitude,
The chirp wave used as the reference wave has the same frequency transition width and pulse width as that of the chirp wave of the transmitted wave, and in order to reduce the side lobe of the pulse compression waveform obtained by cross-correlation with the reflected wave. Considering the frequency characteristics of the probe and the subject, their amplitudes change smoothly at the start point and the end point.

An ultrasonic inspection method according to another aspect of the present invention is the ultrasonic inspection method described above, in which the waveform rises smoothly from the beginning to the center of the waveform and smoothly rises from the center to the end of the waveform. The frequency characteristic of a chirp wave having a falling envelope is obtained and the
Frequency characteristic of the chirp wave, the frequency characteristic of the chirp wave having a conjugate relationship with the chirp wave is obtained, and the second frequency characteristic is used. Further, the frequency characteristic of the chirp wave used for the transmission wave, the probe and the delay material Alternatively, the frequency characteristic of the chirp wave obtained by calculating the product with the frequency characteristic of the ultrasonic wave propagation system including the subject is obtained and used as the third frequency characteristic, and the first frequency characteristic and the first frequency characteristic A chirp wave having a frequency characteristic obtained by dividing the product of the second frequency characteristic and the third frequency characteristic is used as the chirp wave of the reference wave.

An ultrasonic inspection method according to another aspect of the present invention is the above-mentioned ultrasonic inspection method, wherein the chirp wave of the transmitted wave has a rounded shape at the start end and the end of the envelope. . An ultrasonic inspection method according to another aspect of the present invention, in the above ultrasonic inspection method, when determining the frequency characteristics of the ultrasonic propagation system including the probe and the delay material or the test object, a pulse wave as a transmission wave. Is used to obtain the frequency characteristic as the fourth frequency characteristic, and further, the frequency characteristic of the reflected wave from the subject is determined as the fifth frequency characteristic, and the fifth frequency characteristic is referred to as the fourth frequency characteristic. Calculated by dividing by the characteristic.

[0017]

[Function] First, in order to simplify the following description,
The following description will be given. The conversion (Fourier transform) from the representation on the time axis (t) to the representation on the frequency axis (ω) is performed by the function f (t) on the time axis.
And the function F (ω) by the Fourier transform is expressed by the following equation.

[0018]

[Equation 1]

Convolution operation *: Convolution operation

[0020]

[Equation 2]

An ultrasonic flaw detector using pulse compression has a structure as shown in FIG. 16, but in a so-called ultrasonic transmission system from generation of a transmission chirp wave to reception of a reflection echo in a reception amplifier. For example, if the function on the frequency axis of the transmitted chirp wave is S (ω) (the function on the time axis is s (t)), then in the probe until it is amplified by the reception amplifier. Transfer characteristics T (ω) during transmission / reception, material characteristics of subject (attenuation characteristics of ultrasonic waves, etc.)
Due to the influence of M (ω) and the amplification characteristic A (ω) of the reception amplifier, the reflected echo R (ω) becomes (function r (t) on the time axis.
Can be expressed as in equation (7). R (ω) = S (ω) · T (ω) · M (ω) · A (ω) (7)

On the other hand, a window function w _H (t) such as a Hamming-Window (the function on the frequency axis is W
It becomes _H (ω). ), The chirp wave s _H (t) obtained by cutting out the chirp wave s (t) is
It can be expressed as in equations (8) and (9). s _H (t) = s (t) · w _H (t) (8) S _H (ω) = ½π {S (ω) * W _H (ω)} (9) Further, the envelope is The window function of the chirp wave, which is almost constant, is
It corresponds to a rectangular window (rectanguler-Window), but the extraction of the chirp wave by the window function w _R (t) is
Expressions (10) and (11) are obtained. _{s R (t) = s (} t) · w R (t) ... (10) S R (ω) = 1 / 2π {S (ω) * W R (ω)} ... (11)

In equations (9) and (11), 1 /
Since 2π may be omitted formally, it may be omitted, and will be omitted below. Here, the pulse compression (correlation) by the ultrasonic flaw detector by the above-described pulse compression is performed by a process that can be expressed by an equation such as equation (12), and a function z (τ) is obtained.

[0024]

(Equation 3)

In the equation (13), S ^* (ω) is S
It represents the conjugate of (ω). Now, as a condition for obtaining the optimum correlation function z (t), r (t) is s
Equal to (t), that is, the transmitted chirp wave s
This is the case where the autocorrelation of (t) is taken. In reality, since the transfer function in the ultrasonic transfer system acts as a filter, the correlation between s (t) and r (t) deteriorates compared to the self function of s (t). In order to obtain the optimum correlation function, that is, the autocorrelation function of the transmitted chirp wave, it is preferable that the reference wave has a waveform having S _ref (ω) as shown in equation (14).

[0026]

(Equation 4)

Further, as shown in equations (8) and (9), when a chirp wave using a chirp wave window function w _H (t) that suppresses side lobes in autocorrelation is used for transmission, The optimal reference wave is (15) according to equation (14).
It looks like an expression.

[0028]

(Equation 5)

The transmitted chirp wave according to the present invention is (10)
Since it is a kind of rectangular window as shown in the equation (11), the reference wave S _refR (ω) and the received wave R when this function is used
In order to make the cross-correlation of (ω) equal to the cross-correlation in the case of S _H (ω), the reference wave S _refR (ω) as shown in the following expression (16) is obtained.

[0030]

(Equation 6)

Further, in the transmitted chirp wave, if the start end and the end of the envelope are slightly rounded, the miscellaneous noise components in the spectrum are removed as shown in FIG. 17, so that S _refR (ω) is calculated. Waveform deterioration in the course can be prevented. Also, in equation (16),
In order to obtain the transfer characteristic of the ultrasonic transfer system, it is convenient to use a pulse wave whose phase characteristic is linear and whose amplitude characteristic is substantially linear.

[0032]

1 is a functional explanatory view showing an example of an apparatus to which an ultrasonic inspection method according to the present invention is applied. In FIG. 1, reference numeral 41 is a synchronizing section for generating and outputting a necessary synchronizing signal for each circuit, and 42 is an FM signal for setting two types of frequency-modulated signals (chirp signal waves in this example) of two types of predetermined waveforms in different modulation directions. The setting unit 43 is an FM signal transmitting unit that transmits the FM signal read by the signal reading unit 50 that reads either one of the FM signals based on the FM signal set by the FM signal setting unit. , 46 are pulse compression units that perform correlation processing. Reference numeral 47 denotes an FM signal set by the FM signal setting unit 42 and a reflection echo from the subject 4 which is transmitted from the pulse wave setting unit 49 through the signal reading unit 50 and is displayed on the display unit 48 without performing pulse compression. Therefore, a reference wave setting unit that sets a chirp wave having the same modulation frequency and waveform length as the transmission wave, and 48 is a display unit that displays the results correlated by the pulse compression unit.

FIG. 2 is a diagram showing an example of a concrete hardware configuration of the apparatus shown in FIG. In FIG. 2, reference numeral 61 is a personal computer, and the synchronizing unit 41, the FM signal setting unit 42, the FM signal transmitting unit 43, and the pulse wave setting unit 4 of FIG.
9, all functional operations of the signal reading unit 50 and the reference wave setting unit 47 are performed. 62 is a D / A conversion unit, 63 is a transmission amplifier, 64 is a probe, 65 is a subject, 66 is a reception amplifier, and 67 is an A / D conversion unit. 68 is FIR
It is a filter and is concrete hardware of the pulse compression unit 46 of FIG. The FIR filter 68 may have the configuration shown in FIG. 3, for example. 69 is a D / A converter,
70 is an oscilloscope.

In FIG. 2, two types of FM waveforms created by the personal computer 61 and having different frequency modulation directions are converted into analog signals by the D / A converter 62, and the required transmission is performed by the transmission amplifier 63. It is amplified to electric power, and the object 4 is converted into ultrasonic waves from the probe 3.
Will be sent in. The probe 3 and the received signal are signal-amplified by the reception amplifier 66 and sequentially converted into digital signals by the A / D converter 67. Then, the received digital signal is subjected to correlation calculation with the reference wave created by the personal computer 61 by the FIR filter 68, and pulse compression processing is performed. Here, the reason for using the personal computer 61 is that the shape of the transmission / reference wave can be arbitrarily set by changing the program. Furthermore, FIR
The output signal from the filter 68 is converted into an analog signal by the D / A converter 69 and displayed on the oscilloscope 70.

The digital filter shown in FIG. 3 performs digital calculation (equation (17)) which is equivalent to the analog convolution calculation shown in formula (3). Here, as a modification, correlation calculation can be performed ((1
2)), two functions x (n) and y (n) discretized by the A / D converter 67 are converted into analog (1
The convolution operation as shown in the following expression (17) equivalent to the expression (2) can be performed.

[0036]

(Equation 7)

The structure of the digital filter is shown in FIG. The + symbol is an adder, X is a multiplier, and Z ⁻¹ is a delay device, and each delay device delays the calculation result of the multiplier by a time corresponding to the sampling period (ΔT). This digital filter has a reception waveform r (τ) sampled by ΔT.
Between the discretized filter coefficient S (n) and
It is possible to perform the calculation shown in equation (17). In this embodiment, S (n) is 128 coefficients C _{0 to} C ₁₂₇ . Here, the received waveform r (τ) and the filter coefficient C
The operation of the digital filter when _i is set to the waveform as shown in FIG. 3B will be described. The value r (τ ₁ ) of the received waveform input from the input end at a certain time τ ₁ is
It is input to 128 multipliers A _{0 to} A ₁₂₇ , respectively. For example, r (τ ₁ ) input to the multiplier A ₀ is multiplied by the filter coefficient C _0, and the result is the adder D _0.
Is input to Here, the value input to the other of the adder D ₀ is a value obtained by delaying the addition result of the adder D _{1 at} the preceding stage by ΔT by the delay device B ₀ . As the value input to the adder D ₁ , the value r (τ ₁ −1) of the received wave sampled at time (τ ₁ −ΔT) and the multiplication result of C ₁ at A ₁ and the adder D ₂ at the previous stage Is a value delayed by ΔT by the delay device B ₁ . In this way,
The value added by the adder D _i is the time (τ ₁ −i × Δ
The value r (τ ₁ of the received waveform sampled at T)
-I) and a Fitaru coefficient C _i multiplication result and the addition result of the adder D _i-1 to be input to the delay unit B _i in the multiplier A _i, the value input to the adder D _i-1 is Time (τ ₁ −
Received waveform value r (τ ₁ − (i−1)) sampled at (i−1) × ΔT) and the multiplication result of the filter coefficient C _{i−1 in} the multiplier A _i−1 and the delay device B _i− It is the addition result of the adder D _i-2 input to ₁ . That is, the adder D _i
Looking at the value x (i) from the delay device B _i input to, it can be expressed as in equation (19).

[0038]

(Equation 8) Further, the value x (0) from the delay device B ₀ input to the adder D ₀ at the final stage can be expressed as in Expression (20).

[0039]

[Equation 9]

Therefore, the value z output by the digital filter
(Τ ₁ ) can be expressed as in equation (21).

[0041]

(Equation 10)

From the equation (20) and (b) of FIG. 3, in the calculation in the digital filter, the received waveform r (τ) and the filter coefficient C _i are arranged so that the sampling values are arranged in the time axis direction ( In equation (20), r (τ) is arranged in the reverse time axis direction, and C _i is arranged in the forward time axis direction. ) Are multiplied by each other, and the sum is obtained ((c) in FIG. 3).

However, the correlation calculation is performed by the processing shown in the equation (18), but two waveforms s (n) and r (τ) are used.
The time axis directions of are in agreement. If a digital filter as shown in FIG. 3A is used, the filter coefficient C
Equivalent processing can be performed by reversing the array direction of _i with respect to the time axis direction. From (b) of FIG. 3, when a certain time (τ ₁ -117 × ΔT) is replaced with the time τ ₂ ,
r (τ ₁ -127) becomes r (τ ₂ ). 12 from this
The value of the received waveform sampled after 7 × ΔT time is r
(Τ ₂ +127). That is, in order to apply this to the equation (21) and achieve the correlation calculation like the equation (18), the filter coefficients may be rearranged in the opposite direction to the time axis direction ((d) in FIG. 3). ). The arithmetic expression that can be performed as a result is shown in Expression (22). Regarding the development of the correlation calculation using the chirp wave, the reference wave may be introduced into the filter coefficient.

[0044]

[Equation 11]

FIG. 4 is a waveform diagram showing the operation of the correlation calculation between the chirp waveforms of the same frequency modulation and the same pulse width by the digital filter of FIG. 3 (a). The array of each sampling value of the received waveform subjected to the correlation calculation at a certain instant τ ₁ is as shown in (a). Further, the array of the sampling values of the received waveform at a certain moment τ ₂ is (b), the moment τ
The array of sampling values of the received waveform in ₃ is (c). On the other hand, the reference waveform C _{1 to} be subjected to the correlation processing is similarly sampled to form the array (d) of C _{0 to} C ₁₂₇ .
Here, the array of received waveforms (a) and the array of reference waveforms (d)
When the correlation processing shown in the equation (22) is performed, the output timing of the calculation result is the moment when r (τ ₁ +127) is sampled. Regarding the calculation of the equation (22) of the arrays (a) and (c), a low value is shown because there is no correlation because the received waveform is not a reflection echo,
Regarding the calculation of (b) and (c), a high value is shown because the correlation is large. After all, the sampling period ΔT
When the result of the equation (22) obtained for each is viewed as z (τ), a function having a steep main lobe in the vicinity of the reflection echo is obtained.

Here, as one specific example, the thickness is 25 m.
The specimen (STB-N1 standard test piece) on the steel plate of m was inspected. The probe used has a nominal frequency of 5 [MH
z] is a broadband type probe. First, by transmitting a pulse wave (spectrum is shown in FIG. 5B) as shown in FIG. 5A, a bottom surface echo as shown in FIG. 5C is obtained (the spectrum is shown in FIG. (D) of). Here, looking at the spectrum of the pulse wave ((b) of FIG. 5),
The shorter the pulse width, the flatter the straight line (Fig.
(B) has a solid line), but in reality, it has a finite pulse width, and therefore has a shape like the dotted line in (b). Further, the waveform shown in (c) of FIG. 5 is a waveform corresponding to R (ω) in the equation (7) on the frequency axis, but since the transmission wave S (ω) is a pulse wave, “S” (Ω) = 1 ”, and the bottom echo can be regarded as T (ω) · M (ω) · A (ω). Further, in order to eliminate the influence of noise around the echo, only the echo was cut out and this waveform was used as the transfer characteristic in the ultrasonic wave transfer system ((e) and (f) in FIG. 5).

The chirp waveform used for transmission is shown in FIG.
Shown in The waveform of the transmission chirp waveform shown in (a) of FIG. 6 that has passed through the already-known filter having the transfer characteristics of the ultrasonic transmission system shown in (e) and (f) of FIG. It is a waveform shown in (b). The spectrum is shown in FIG. 6 (c). Here, the received wave R (ω) when the transmitted chirp wave S _R (ω) is used for S (ω) in the equation (7)
Is a function shown in (b) and (c) of FIG. From this, using the Hamming window shown in equation (8) as the window function, (1
When the reference wave S _refR (ω) shown in the equation (6) is _calculated ,
It becomes a reference wave like (d). As a result of performing correlation between this reference wave and the above-mentioned transmitted wave, a correlation function z (t) as shown in FIG. 6 (e) was obtained. Compared with the conventional correlation function ((f) of FIG. 6) obtained by transmitting the chirp wave through the Hamming window, both the side lobe and the main lobe wave numbers are reduced and the pulse compression effect is improved. Is recognized.

[0048]

As described above, according to the present invention, the reduction of the transmission energy accompanying the application of the window function aiming at the reduction of the side lobe is compensated, so that the reduction of the transmission energy is avoided and Since the transfer characteristics of the ultrasonic wave transmission system such as the sample can be included in the reference chirp wave, it is possible to use different probe conditions such as the type of probe, variations in the material characteristics of the subject and variations in the amplifier characteristics of the flaw detector. Since the waveform variation due to different ultrasonic transmission systems can be corrected, the optimum pulse compression waveform can always be obtained. this is,
It is an effective means not only for improving the flaw detection accuracy, but also as one approach for the quantitative determination of flaw detection results.

[Brief description of drawings]

FIG. 1 is a functional configuration diagram of an apparatus to which an ultrasonic inspection method according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an example of a specific hardware configuration of the apparatus of FIG.

FIG. 3 is a diagram showing a configuration example of the FIR digital filter of FIG.

FIG. 4 is a diagram for explaining the operation of FIG.

FIG. 5 is an explanatory diagram of various waveforms in the above embodiment.

FIG. 6 is an explanatory diagram of various waveforms in the above embodiment.

FIG. 7 is a functional configuration diagram of a conventional general ultrasonic flaw detector.

FIG. 8 is an explanatory diagram of a flaw detection waveform obtained by flaw detection using a conventional general ultrasonic flaw detector.

FIG. 9 is a functional configuration diagram of a conventional general ultrasonic flaw detector.

FIG. 10 is an explanatory diagram of a flaw detection waveform obtained by flaw detection using a conventional general ultrasonic flaw detection apparatus.

FIG. 11 is a diagram illustrating the principle of correlation processing.

FIG. 12 is a functional configuration diagram of a conventional general ultrasonic flaw detector.

FIG. 13 is an explanatory diagram of a problem of flaw detection using a conventional general ultrasonic flaw detection method.

FIG. 14 is an explanatory diagram of a problem of flaw detection using a conventional general ultrasonic flaw detection method.

FIG. 15 is an explanatory diagram of a problem of flaw detection using a conventional general ultrasonic flaw detection method.

FIG. 16 is a diagram illustrating an ultrasonic flaw detection method according to the present invention.

FIG. 17 is an explanatory diagram of a flaw detection waveform obtained by the ultrasonic flaw detection method according to the present invention.

Claims (4)

[Claims] 1. A chirp wave whose frequency transits within a predetermined pulse width is transmitted as a transmitted wave into a subject through a probe, and the received wave obtained through the probe and a preset wave In the ultrasonic inspection method of performing a correlation process with a reference wave composed of a chirp wave and grasping the state of the subject by the pulse-compressed signal after the correlation process, the amplitude of the chirp wave used as the transmission wave is The chirp wave used as the reference wave is constant, its frequency transition width and pulse width are the same as those of the chirp wave of the transmission wave, and its amplitude changes smoothly at the start point and the end point, respectively. An ultrasonic inspection method characterized by: 2. A frequency characteristic of a chirp wave having an envelope that smoothly rises from the start portion to the center portion of the waveform and smoothly falls from the center portion to the end portion of the waveform, and obtains it as the first characteristic. A frequency characteristic, a frequency characteristic of a chirp wave having a conjugate relationship with the chirp wave is obtained, and is used as a second frequency characteristic. Further, the frequency characteristic of the chirp wave used for the transmission wave, the probe, and the delay material. Alternatively, the frequency characteristic of the chirp wave obtained by calculating the product of the frequency characteristic of the ultrasonic wave propagation system including the subject is calculated and used as the third frequency characteristic, and the first frequency characteristic and the A chirp wave having a frequency characteristic obtained by dividing a product with a second frequency characteristic by the third frequency characteristic is used as a chirp wave of the reference wave. The ultrasonic inspection method according to claim 1. 3. The ultrasonic inspection method according to claim 1, wherein the chirp wave of the transmitted wave has a rounded shape at the start end and the end of the envelope. 4. When obtaining the frequency characteristic of an ultrasonic wave propagation system including the probe and the delay material or the subject, a pulse wave is used as a transmission wave to obtain the frequency characteristic, and then the fourth frequency characteristic is obtained. Further, the frequency characteristic of the reflected wave from the subject is obtained, the fifth frequency characteristic is used as the fifth frequency characteristic, and the fifth frequency characteristic is divided by the fourth frequency characteristic. The ultrasonic inspection method according to 2 or 3.